This invention relates generally to an improved quartz crystal oscillator circuit for use in an electronic timepiece and especially to a monolithic integrated quartz crystal oscillator circuit for stabilizing the oscillating frequency thereof during changes in the supply voltage. Heretofore, certain problems have existed in quartz crystal oscillator circuits formed from complementary coupled MOS transistors. In particular, significant changes in the frequency of such circuits were caused by changes in the supply voltage. Similarly, when the supply voltage of the quartz crystal circuit were stabilized, variations in the threshold voltage of the MOS field effect transistors used would also effect a substantial change in the frequency thereof. The change in frequency was caused by a reduction in the output impedance of the inverter formed by the complementary coupled P-channel and N-channel transistors which were reduced in proportion to the increase in the supply voltage and/or threshold voltage.